False Negatives in India Raise Pandemic Concerns
Recombinomics Commentary 15:30
February 5, 2008
There are no cases of bird flu infection among the people in West Bengal but the government has banned the movement of poultry and its marketing across the state for three months from today till further orders as a precautionary measure.
Blood samples of all the 23 cullers who had fallen sick had tested negative.
The above comments on negative blood samples from cullers in West Bengal continue to raise concerns. It is unclear why blood samples are being used, since PCR, sequencing, and viral isolation tests use swabs, usually from the nose or throat. H5N1 has rarely been isolated from blood samples, and isolation is usually from advanced patients. Detecting H5N1 in blood samples from patients on Tamiflu would be difficult.
WHO has a team on the ground in Karachi, and they have requested collection of nasal and throat swabs from the cullers in isolation there, discounting negative data from blood samples.
The level of H5N1 in West Bengal has been high (see satellite map here and here, and high risk activities by villagers, including eating dead birds and handling dead birds without PPEs, have been well documented. Therefore the likelihood of no human H5N1 infections is low.
Recently, H5N1 sequences from Pakistan’s northwestern region were released. The 2006 and 2007 were related to each other and most closely related to sequences from Afghanistan. However, the sequences were clade 2.2.3, as were 2006 sequences from India. Although neither India nor Bangladesh have released 2007 or 2008 sequences, these sequences, like the Pakistan sequences, are almost certainly clade 2.2.3. Clade 2.2.3 isolates in 2006 also caused human infections in Azerbaijan, providing additional support for human cases in India.
India also failed to detect human cases linked to the 2006 outbreak in the west. Like wild birds, which clearly are H5N1 positives, India has never reported a positive in a human sample.
These failures to detect H5N1 in exposed populations raise concerns over monitoring the spread of H5N1 to contacts. A long sustained H5N1 transmission chain was reported in Pakistan, and similar transmission would be missed in India because of the testing procedures, which fail to detect H5N1 in human or wild bird samples.
These failures increase pandemic concerns.
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